A car using an internal combustion engine using gasoline or heavy oil as main fuel has a serious effect on environmental pollution, such as air pollution, or the like. Therefore, many attempts to develop an electric car or a hybrid car have been recently conducted so as to reduce the generation of pollution.
In recent years, a high-output secondary battery using a high energy density non-aqueous electrolyte has been developed.
A large-capacity secondary battery is configured by connecting a plurality of high output secondary batteries in series so that the large-capacity secondary battery may be used for devices requiring large power for driving a motor, such as an electric car, or the like.
As such, in a single large-capacity secondary battery (hereinafter, referred to as a ‘battery’), a plurality of cells are connected to one another in series or in parallel.
In this case, the battery is provided with the electrode tab for electrically connecting the plurality of cells to one another, wherein the plurality of cells are connected to one another by using various methods, such as clip, crimping, welding, bolt fastening, or the like.
Among those, FIG. 1 is a diagram showing a welding method according to the related art. The welding method according to the related art shown in FIG. 1 performs welding in a direction vertical to surfaces of welding portions 21 of the electrode tab 20 after the welding portions 21 of the electrode tab are positioned so as to overlap with each other by being bent in a direction vertical to the cells 10.
However, the welding method shown in FIG. 1 cannot easily weld at least three sheets of tabs, connect the tabs in a parallel structure, and weld the tabs to which a cell sensing line, or the like, is added.
In addition, in the case of a laser welding method, a laser spot size is only about 230 μm. Therefore, a portion to be welded should be within the laser spot size, which results in greatly degrading mass production during a module assembling process.
Accordingly a need exists for the development of a battery module and an electrode tab welding method capable of simplifying a welding method and a manufacturing process so as to increase mass production.